Conventional progressive addition lenses are one-piece lenses having an upper viewing zone (“the distance zone”), a lower viewing zone (“the near zone”), and a progressive corridor (“the intermediate zone”) therebetween which provides a gradual power progression from the distance zone to the near zone without any dividing line or prismatic jump.
Although early progressive ophthalmic lenses were somewhat crude in design, they have consistently improved in performance over the past few decades. The improvement in performance has been a causative factor in significantly increasing patient demand for these categories of lenses to the point where lens dispensers and manufacturers today offer a large number of different progressive lens designs. There is thus available to a dispenser a large number of lens designs that may be dispensed to a wearer.
One way of dispensing a progressive ophthalmic lens element for a lens wearer involves selecting a semi-finished progressive ophthalmic lens element from a series of semi-finished lens elements. Generally speaking, each lens element in a series of semi-finished progressive ophthalmic lens elements has a progressive front surface having a range of progressive surface parameters and a spherical back surface.
Since lens wearer's experience different levels of presbyopia, different designs of semi-finished lens elements are provided for different addition powers, typically from 0.75 D to D in 0.25 D increments (that is, twelve different lens designs for each series). Furthermore, a single product intended as a general purpose solution for presbyopia needs to be able to correct vision for a wide range of prescriptions, typically between −10.00 D and +6.00 D or more. However, since a single base curve can ensure satisfactory optics only over a range of prescription powers much narrower than is required, lens manufacturers typically create a range of lens element series or base curves to satisfy this requirement.
Typically, there may be between four and eight lens series in a progressive addition lens (PAL) product. Again, each series typically includes progressive ophthalmic lens elements, or lens designs, having a particular base curve and a range of addition powers. Thus, and in relation to a dispensing process that starts with the selection of a semi-finished lens element, one prior art process involves selecting a lens element series having a base curve that is recommended for a lens wearer's distance vision requirements, and then selecting, from within that series, a lens element having an addition power that is suitable for a lens wearer. Finally, the selected lens element is then finished, by adding a prescription surface, so as to provide a finished progressive ophthalmic lens element that meets the prescription requirements of the lens wearer.
Unfortunately, progressive ophthalmic lens elements included in a series of semi-finished lens elements are somewhat restricted in that for each “base curve” series, only a single progressive ophthalmic lens element, and thus a single progressive surface design, is available for each addition power. Therefore, the progressive surface of each progressive ophthalmic lens element in the series may not be optimised for a particular lens wearer. Recently, progressive ophthalmic lenses have been developed that are able to be produced by a free-form process that avoids the need to modify a semi-finished lens element. In progressive ophthalmic lenses of this type, the multi-focal and prescription surface may be combined on the same lens surface (for example, the back surface), or different lens surfaces (for example, the front and back lens surfaces).
The selection of a particular progressive ophthalmic lens element from a range of progressive ophthalmic lens elements available for an individual wearer, and the subsequent fitting of the selected lens element to a frame to form spectacles for use by the wearer, are of critical importance to the effectiveness of, and thus the lens wearer's satisfaction with, the resultant spectacles.
Unfortunately, given the large number of progressive ophthalmic lens products on the market and the almost infinite combinations and permutations of the design parameters, and the variety of tasks for which a lens may be used, selecting a lens design (from a dispensers perspective) or designing a lens (from a designers perspective) which is suitable for an individual wearer's needs has proven to be somewhat difficult. Therefore, when selecting a progressive lens for a wearer, many dispensers miss the opportunity to fit a lens which has been selected on the basis of the wearer's needs because they instead fit a favourite, trusted lens design.
It would be useful to provide an array of progressive ophthalmic lens elements having a progressive lens design that is attributable to, or associated with, a value, or category of, a lifestyle and biometric parameters of a lens wearer so as to thereby assist a dispenser to at least recommend a suitable progressive ophthalmic lens element from the array based upon lifestyle and biometric information provided by, or obtained from, a lens wearer.